1. Field of the Invention
The invention is directed to an improved method for applying an electrical insulation to a ferromagnetic body, provided with axial slots for receiving an electrical winding, of a primary element of an electrical machine a slotted armature body of an armature of a direct-current motor.
2. Description of the Prior Art
A slotted armature body of an armature of a direct-current motor of the type with which this invention is concerned includes a plurality of profiled laminations, which are lined up axially one after the other and joined to make a lamination packet which is press-fitted onto an armature shaft. The armature body has a plurality of axial slots, which are open to both face ends of the cylindrical armature body 10 and which discharge at a slot opening in the cylindrical surface of the armature body. An armature winding in the form of coils is wound into the axial slots. The coils are wound from an insulated coil wire, such as painted copper wire. Before the armature winding is wound in place, the axial slots and also the face ends of the armature body are provided with an electrical insulation.
In the possible methods for applying such an insulation to the slots, coating the armature body with electrostatically charged plastic powder has proven itself as the most economical method, with the additional advantage that the slot cross section is reduced only insignificantly by the insulation, and a quite high slot fill factor for the armature winding can thus be achieved.
In a known method for applying the electrical insulation to the armature body by means of electrostatic powder coating, the armature body already pressed together with the armature shaft is precleaned to eliminate contamination occurring in manufacture; masked at points that are not to be coated, such as the armature shaft; and coated in a powder fluid bath with electrostatically charged plastic powder. The masks additionally take on a clamping function for fixing the armature body on a conveyor system that passes through the fluid bath, and for this purpose the armature bodies have to be repositioned on the conveyor system after masking. The bottom of the fluid bath comprises a porous plate, through which ionized or in other words electrically charged compressed air flows, which electrostatically charges the powder uniformly and fluidizes the powder, so that the powder behaves like a fluid. The electrostatically charged powder particles, because of the charges that are opposite the force of attraction, settle on the armature bodies being guided through the fluid bath and remain stuck to them. The thus-coated armature bodies are cleaned outside the fluid bath in a further method step, to remove powder adhering to the cylindrical surface of the armature bodies. Next, the cleaned armature bodies are delivered to a heating section, in which by heat input, the powder layer is melted and fired and hardened. The armature bodies are repositioned again and unmasked in a further method step. The unmasked armature bodies are then cooled down in a cooling zone. The removed masks are delivered to a mask cleaner, and with the cleaned masks, new, precleaned armature bodies are masked. The cooled-down armature bodies are removed from the processing system and delivered to an automatic winder.
This method produces a thin insulation layer, approximately 50 to 100 μm thick, in the axial slots with good thermal and electrical properties, but has decisive disadvantages in terms of costs. For instance, the fluid bath requires a horizontal position of the armature bodies, which in the rest of the production process are usually processed vertically, so that as the method progresses, the armature bodies have to be repositioned multiple times. Moreover, a quite complicated conveyor system is required for feeding the armature bodies through the fluid bath. If damage occurs in the fluid bath, replacing the fluid bath that is integrated into the system is extremely time-consuming and leads to expensive system down times. The masks also take on the function of clamping the armature bodies while they are being conveyed. If the masks become worn, inadequate clamping of the armature bodies can occur, which threatens the course of the process and leads to down times.